1. Field of the Invention
The present invention relates generally to a method of manufacturing magnetic powder and is directed more particularly to a method of manufacturing magnetic iron oxide powder covered by cobalt and/or a cobalt compound suitable for use with a high density magnetic recording medium.
2. Description of the Prior Art
Recently, a cobalt containing magnetic iron oxide powder suitable for high density magnetic recording, has been developed. The magnetic powder proposed by the prior applicant in the application (Japanese Patent Application No. 79645/1977 which corresponds to the U.S. patent application Ser. No. 67,036 filed Aug. 16, 1979 which is a continuation application of U.S. Application Ser. No. 921,753 filed July 3, 1978) is characterized by the fact that cobalt is not diffused within the magnetic powder but is coated on the surface of the magnetic powder in the form of cobalt and/or a cobalt compound to make a magnetic powder with high coercive force, lower demagnetization caused by pressure and heat, and lower print through i.e. superior in print through effect.
In the method of manufacturing such kinds of magnetic powders proposed in my prior application, a cobalt salt is used as the starting material. Aqueous solution of this cobalt salt is mixed with an alkaline solution to form cobalt hydroxide Co(OH).sub.2 and then deposited on the surface of the magnetic powder. Generally speaking, cobalt hydroxide has a tendency to form a gel. In this case, it is rather difficult to deposite the cobalt hydroxide uniformly on the surface of the magnetic powder without gelation of the cobalt hydroxide.